The present invention relates to a variable geometry turbine. The preferred, but not exclusive, field of application of the invention is in superchargers of internal combustion engines, to which reference will be made in the following description in a non-limiting manner.
Turbines are known that comprise a spiral inlet channel surrounding the rotor of the turbine and a vaned annular nozzle interposed radially between the inlet channel and the rotor. Variable geometry turbines (VGT) are also known in which the vaned annular nozzle has a variable configuration so that flow parameters of the operating fluid from the inlet channel to the rotor can be varied. According to a known embodiment, the variable geometry nozzle comprises an annular control member moving axially to vary the throat section, i.e. the working flow section, of this nozzle. This annular control member may be formed, for instance, by a vane support ring from which the vanes extend axially and which can move axially between an open position in which the vanes are immersed in the flow and the throat section of the nozzle is maximum, and a closed position in which the ring partially or completely closes the throat section of the nozzle. During the forward movement of the ring, the vanes of the nozzle penetrate through appropriate slots in a housing provided in the turbine housing in a position facing this ring.
The displacement of the annular control member is controlled by means of a control device comprising an actuator external to the turbine, of pneumatic or electrical type, and a kinematic chain of transmission of motion from the actuator to the annular control member of the nozzle. This entails relatively high costs and may limit reliability. In most known solutions, the accuracy of the control is also reduced, since the kinematic chain has significant play which tends to increase during the life of the device as a result of wear. A further drawback connected with known solutions lies in the fact that known control devices require very precise adjustment which is a delicate operation.
The object of the present invention is to provide a variable geometry turbine with a vaned nozzle provided with an axially moving control member which is free from the drawbacks connected with known turbines and described above.
This object is achieved by the present invention which relates to a variable geometry turbine comprising a housing, a rotor supported in a rotary manner in this housing, the housing defining an inlet channel for an operating fluid in the form of a spiral surrounding the rotor, and an annular vaned nozzle of variable geometry interposed radially between the channel and the rotor and comprising a control member moving axially in order to control of the flow of the operating fluid from the channel to the rotor by varying a throat section of the nozzle, characterised in that the control member is formed as an annular piston of a fluid actuator, the turbine comprising a fluid control line, the control member being actuated directly by means of a control pressure via this fluid control line.